Just a brief note (for now) on what looks to be a fascinating discovery. Scientists from the British Antarctic Survey have discovered previously unknown underwater volcanoes in Antarctica. During research cruises in RRS James Clark Ross the BAS team discovered no fewer than twelve sub-sea volcanoes, some up to 3 km high, with at least one showing signs of recent activity. The volcanoes were identified in the Southern Ocean near the South Sandwich Islands, using shipboard 3D seafloor mapping technology.

Dr Tamsin Mather is a volcanologist in the Department of Earth Sciences at the University of Oxford (here’s her departmental web page). Dr Mather will be talking about her research at the Cheltenham Science Festival this week (ugly web page here), and gives a summary of what volcanology is, how it is done and what she in particular has been up to in this excellent BBC News audio slideshow — a miracle of concision at under five minutes, with great images and an accessible, informative expert commentary. Highly recommended.

We all know that volcanic arcs are related to subduction zones: the areas of the Earth’s surface where an oceanic lithospheric plate comes up against another plate and moves beneath it, ultimately being re-absorbed into the mantle in a vast geological recycling scheme. The oceanic rock is full of water, which begins to be released as it reaches greater depths and becomes subject to increased heat and pressure, entering the overlying mantle wedge that lies between it and the continental lithosphere and lowering its melting point, producing melt that ascends to feed volcanoes above the subduction zone. In offshore island arcs and continental volcanic arcs the line of volcanoes is always offset some way from the point at which the subducted plate makes its dive, which is marked by an oceanic trench.

Various explanations have been put forward for why the volcanoes appear where they do, usually connected to theories as to the locations of the points of highest temperature in the zone where the upper surface of the subducted slab and the mantle wedge are in contact with each other. No-one has really got to the bottom of it, however (so to speak). But two researchers from the University of Oxford Department of Earth Sciences, Philip C. England and Richard F. Katz, have been working on this problem in a new way, by applying a mathematical model of heat transport in this zone to establish where the areas of highest temperature, and thus of melt production, occur. Their conclusion is that the locations of subduction zone volcanoes can only be explained if they emerge above regions in which mantle is melting in the absence of water. Hydrous melting — melting associated with the presence of water — pervades the mantle wedge, but the conventional models of arc formation suggest that there is a particular point at which the degree of hydrous melting increases rapidly because of conditions of temperature and/or pressure, and that the arc front forms above this point. Yet these processes of hydrous melting occur not in a restricted area of the wedge but across a broad region of the mantle core, raising the issue of how the melt then becomes concentrated to feed a relatively narrow volcanic arc. England and Katz avoid that difficulty by invoking the crystallization of rising magma as it reaches the thermal boundary layer at the top of the wedge. This deflects the magma back towards the trench and into the ‘nose’ of the mantle wedge, whence it makes its way upwards by thermal erosion, opening pathways for hydrous melt which drives the volcanism of the arc.

The paper, ‘Melting above the anhydrous solidus controls the location of volcanic arcs’ by can be found in the 7 October 2010 issue of Nature. It’s subscribers only of course: the link below will give you the abstract, to read further you need to log in or pay up.

Dominating the landscape to the west of El Salvador’s capital of San Salvador is the massive volcano that shares the city’s name. San Salvador volcano last erupted in 1917, the beginning of the eruption being marked by an earthquake estimated to have been magnitude 5.6 which left up to 90% of the capital’s housing stock damaged or destroyed according to contemporary reports (see today’s Daily Volcano Quote). The 1917 eruption, the seat of which was El Boquerón, the main summit of San Salvador, lasted from June to November and produced extensive lava flows and ashfall, damaging crops and causing some fatalities in the surrounding region.

Today the city of San Salvador has a population estimated at 2.2 million and its suburbs encroach upon the lower slopes of San Salvador volcano. A fresh eruption of San Salvador on almost any scale would have serious consequences for the city of San Salvador. Even without any eruptive activity, the volcano’s unstable slopes pose a significant landslide hazard for the surrounding areas.

The authorities in El Salvador are very conscious of the hazard San Salvador poses. Yesterday the Salvadorean newspaper El Diario Co Latinoreported that the Salvadorean environment ministry, the Ministerio de Medio Ambiente y Recursos Naturales (MARN) has been working with geologists and non-governmental organizations from across the world to assess the potential threat of San Salvador and plan hazard mitigation and response strategies. Taking into account San Salvador’s 3000-year history of frequent activity, ‘The likelihood that a phenomenon such as that of 1917 will occur within the next 100 years is high, but it is not possible to give an exact time range’, says volcanologist Dolores Ferrés, author of the study Estratigrafía, geología y evolución del volcán de San Salvador: Aplicación en la evaluación de peligros volcánicos y su posible impacto, which was presented to the media at a congress held by MARN on 21 September.

Ferrés’s study is described in a news release from El Salvador’s Servicio Nacional de Estudios Territoriales (SNET) as ‘a breakthrough in the generation of knowledge about volcanic risk in the country and providing vital information to decision-makers in various sectors’. The intention is to carry out a comprehensive hazard assessment programme for San Salvador volcano and the surrounding area. ‘Although the volcano currently shows only very week activity (fumaroles in Cerro La Hoya and very sporadic volcanic-tectonic seismicity) it is considered one of the most dangerous volcanoes in Central America because of its proximity to large urban areas and its eruptive history’, is the SNET’s current verdict on San Salvador volcano.

The study looks at the emplacement of thirteen magmatic dykes in north-eastern Ethiopia between 2006 and 2009. A rift zone produced by the spreading boundary between the African and Arabian plates runs through this region; most such rift zones are situated on the ocean floor, so this remote area provides a valuable opportunity to study the processes associated with spreading plate boundaries without getting one’s feet wet. A team led by Ian Hamling of Leeds University measured changes in ground tension associated with each successive dyke emplacement, and found that subsequent eruptions were most likely in locations where the tension had been increased. Although the initial level of stress along a rift zone that becomes active is unknown, measurements of stress transfer will reveal whether eruptions in one location cause compressive stress change (clamping) or tensile stress change (unclamping) elsewhere. New dyking would be expected in locations subject to unclamping – in other words, where the ground has been stretched and is under increased tension – and the study shows that such is indeed the case: ‘the mean percentage of opening in unclamped sections of the rift has been 70%, with seven of 12 dykes having over 75% of their opening in regions unclamped by the previous intrusion’. The study concludes: ‘This result indicates that the stress change, induced by a new dyke, is a controlling factor on the location of future events and should therefore be incorporated into routine volcanic hazard monitoring’.

A fascinating article in Science News, magazine of the Society for Science and the Public, explores the role of ice in volcanism with particular reference to the eruption of Iceland’s Eyjafjallajökull earlier this year. When Eyjafjallajökull erupted on 20 March 2010 it began with a fissure eruption characterized by relatively quiet effusive activity and limited ash emissions. This changed in mid-April when the seat of the eruption moved west to an area beneath the ice-cap. As the eruption became sub-glacial, explosivity and ash production increased, with the disruptive consequences that we are all familiar with.

The Science News article, an excellent piece of work by Alexandra Witze, looks at some of the research that is now going on in the wake of the Eyjafjallajökull eruption to explore the crucial issue of glaciovolcanism – the interaction between volcanic activity and ice.

Eyjafjallajökull’s eruption has refocused attention on a small but rapidly growing subset of volcanology: the study of volcano-ice interactions. Ice-covered volcanoes, or “glaciovolcanoes,” are not fundamentally different from other volcanoes in terms of plumbing or eruptive style. But they distinguish themselves the moment magma breaks through the crust and meets ice.

One reason to study icy volcanoes is to better understand their risks. Nobody died in the Eyjafjallajökull eruption, but in 1985 an eruption beneath an icy mountain in the Colombian Andes sent massive mudflows coursing downstream, killing more than 20,000 people. Dozens of volcanoes mantled with ice are scattered around the world, each posing a distinct hazard.

The volcano responsible for that killer eruption of 1985 was of course Nevado del Ruiz; the 25th anniversary of that event will be on 13 November this year. At Nevado del Ruiz human failings in monitoring and communication (along with unfortunate weather conditions that obscured the summit) rather than geology were to blame for the scale of the disaster, but the eruption certainly illustrates the particularly hazardous nature of ice-capped volcanoes.

‘Rumbles hint that Mount Fuji is getting angry’, says the rather sensationalized headline that New Scientist has stuck over their report of a new study of Mount Fuji. There’s no suggestion in the original research paper that Fuji is ‘getting angry’, or even slightly annoyed, just a new theorization of the processes that may be causing Fuji’s magmas to become more andesitic to dacitic, thus tending towards a more explosive eruptive style.

The paper, ‘Crypto-magma chambers beneath Mt. Fuji’ by Takayuki Kaneko et al (JVGR 2010, in press) notes that Fuji’s eruptive history has been characterized by basaltic activity with occasional explosive eruptions involving andesitic to dacitic lavas. Studies of Fuji’s lavas using air-fall scoria, however, indicate an increase in silica content over time: Kaneko proposes a two-level magma chamber system to account for this, with basaltic magma at the deep level and more silicic magma at the shallower level. The increasing level of silica, suggests Kaneko, ‘could result from the combination of repeated magma mixing between the two end-member magmas and fractional crystallization processes in each magma chamber’.

The upward trend of SiO2 … seems to continue to the present. In the last several thousand years, explosive eruptions involving a small volume of andesitic magma were repeated sporadically … Such andesitic or dacitic products have not been found from the older periods of Fuji–Ko-Fuji to the middle stage of Shin-Fuji volcanoes. This may suggest that, in the last several thousand years, the composition of the magma in the shallow chamber has become more SiO2-rich than ever.

The New Scientist article says that Kaneko interprets the low-frequency earthquakes detected beneath Fuji in 2000 and 2001 as possible evidence for magma injections into the lower chamber, ‘and adds he would not be surprised if Fuji erupts in the very near future’. That’s the ‘Fuji getting angry’ bit, and it’s stretching things somewhat on the basis of this research. The paper itself simply concludes with the suggestion that ‘Fuji may have entered a stage with the potential for explosive eruptions involving andesitic to dacitic magmas’.

Giant impact near India – not Mexico – may have doomed dinosaurs (Sankar Chatterjee, Texas Tech University) – the Shiva basin off the west coast of India may be a meteorite impact crater: as well as killing off the dinosaurs, the crust-vaporizing bang could have enhanced the Deccan Traps eruptions.

The Geological Society of America is currently holding its 2009 Fall Meeting in Portland, Oregon (18-21 October 2009) and with volcanoes featuring prominently in its title, ‘From volcanoes to vineyards – living with dynamic landscapes’, it’s no surprise that there are plenty of volcanic topics in the programme.

Information on particular presentations is regularly updated on the Portland meeting news release page, but as a service to those chiefly interested in things volcanic (and who don’t feel like working their way through the list opening PDF after PDF) I will be summarizing the volcano-related stuff here.

This first post lists contributions from United States Geological Service scientists: the source is this USGS PDF.

Can static decompression of magma trigger volcanic eruptions? (Michael Poland, USGS) – the March 2008 explosion at Kilauea may have been triggered by static decompression caused by lava withdrawal from a reservoir beneath the summit caldera: a mechanism that has implications for volcanic hazards worldwide.

A major explosive eruption and aftermath in the Aleutians (Chris Waythomas, USGS) – the geomorphic and ecological impact of the 2008 Kasatochi eruption, particularly in relation to seabirds.

The Los Tuxtlas region consists of an isolated range of volcanic mountains in southern Mexico, in the central southern area of the coastal state of Veracruz. The isolation of this elevated region has given it a virtual island ecosystem, enabling flora and fauna to flourish there in the most northerly tropical rainforest environment on the American mainland. In 1998 a nature reserve was established there by the Mexican Government, the Reserva de la Biósfera Los Tuxtlas.

So, it’s a very interesting part of the world. Yet while the flora and fauna of Los Tuxtlas have been extensively studied, the geology of the region has been somewhat neglected: which is unfortunate, not only because of the intrinsic geological interest of this anomalous volcanic belt, but because it is region of active volcanism. Volcán de San Martín, the dominant volcanic edifice of the Tuxtla volcanic field, last erupted in 1793 (VEI=4) and 1794 (VEI=2), if more recent uncertain reports of activity are disregarded.

However, a detailed study of volcanic activity and potential hazards in Los Tuxtlas is now under way, reports the Veracruz newspaper El Golfo (drawing upon a report in the Mexican university periodical UniVerso). A team of experts from the Universidad Veracruzana are working to compile a detailed hazard map of Los Tuxtlas which will help local authorities plan for better civil protection:

In addition to studying past eruptions and estimating future ones … [the team] will assess the hazards faced by local communities through mud and debris flows generated by the rains and storms that constantly sweep the region with its abundant vegetation and proximity to the sea.

In communities of Pajapan municipality important effects have already occurred, including the loss of human life because of debris flows caused by the heavy rains, comments Sergio Rodriguez Elizarrarás, an expert in geology and volcanology from the Centro de Ciencias de la Tierra (CCT). ‘What we want is that these tragedies are not repeated’.

The project involves mineralogical and soil studies throughout the Tuxtla volcanic complex, and detailed study of the little-known eruptive history of San Martín volcano. Funding for the project, to the tune of more than 4 million pesos (around $300,000 or €200,000), is being provided by the Mexican Government’s Fondo Nacional de Prevención de Desastres Naturales (Fopreden).

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